NEW ORLEANS — First came the storm. Then came the workers. Now comes the baby boom.

In the latest twist to the demographic transformation of New Orleans since it was swamped by Hurricane Katrina last year, hundreds of babies are being born to Latino immigrant workers, both legal and illegal, who flocked to the city to work on the reconstruction.

The throng of babies gurgling in the handful of operational maternity wards here has come as a big surprise — and a financial strain — to this historically black and white city, which before the hurricane had only a small Latino community and virtually no experience of illegal immigration.

"Of all the myriad things that have changed after Katrina, this wasn't high on anybody's priority list," said Dr. Mark Peters, chief executive of East Jefferson General Hospital in Metairie.

Because many immigrant mothers cannot afford to pay for prenatal care or delivery services, New Orleans's newest citizens are adding an unexpected load to the decimated health infrastructure in a city abandoned by many of its doctors. Much of the state-financed Charity Hospital system, which before Hurricane Katrina provided the bulk of care to New Orleans's uninsured and indigent population, remains closed.

Lacking health insurance and barred from most government assistance, expectant immigrant mothers can go to only the handful of charitable clinics that are still operating and that do not question a woman's immigration status when offering low-cost prenatal care.

The two health units providing prenatal care run by the Louisiana Department of Health and Hospitals saw more than 1,200 pregnant women from January to mid-November. Virtually all were Latino immigrants.

"Before the storm, only 2 percent were Hispanic; now about 96 percent are Hispanic," said Beth Perriloux, the head nurse in the department's health unit in Metairie.

There are so many pregnant women that the clinics have reached capacity. Dr. Erin Brewer, the department's medical director, said, "We've gone from having a maternity clinic two to three days a week to five days a week."

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Many immigrant women are forgoing prenatal care and showing up, ready to deliver, in hospital emergency rooms, where they are required to be seen even if they are in the country illegally. "When I felt the pains I just went to the women's and children's hospital," said Noemi, an illegal immigrant from Oaxaca, Mexico, who arrived in New Orleans right after the storm as part of a cleaning crew from North Carolina. She left the city but then returned in October, a month after giving birth to her daughter Alejandra in Lake Charles, 200 miles, or about 320 kilometers, to the west.

According to the Louisiana Health and Population Survey, released in November, the number of Latinos living in households in Orleans and Jefferson parishes has increased by about 10,000 since 2004, to 60,000, even as the total population has fallen by about a quarter, to roughly 625,000.

Last summer, researchers at Tulane University estimated that there were 5,000 to 7,000 illegal Latino workers in Orleans Parish alone, excluding nonworking relatives. But some community workers estimate that tens of thousands have arrived since the storm.

Most are not new to the United States. They come from Texas, Florida or California, seeking construction work, which can pay $150 a day. But there are some newcomers, including Sara Alvarado, a 26-year-old Honduran, who arrived in the United States in August after a monthlong odyssey through Mexico with her partner, Tony, 32.

When Alvarado finally got to New Orleans, brought into the country by coyotes, or smugglers, who charged $6,000, she was more than six months pregnant.

The last time she had seen a doctor was four months before.

"The coyotes wanted to charge me more and bring me across in a car," Alvarado said, sitting in her cramped home in the Upper 9th Ward that she and Tony share with four other people.

"But I didn't take a single vitamin, and I came across that desert jumping fences and all that, and look, here is this boy," she said cradling her son, Jackson Antonio, an American citizen who came into the world at Tulane-Lakeside Hospital on Oct. 17, the day the 300 millionth American was born.